1. Field of the Invention
Embodiments of the invention relate generally to methods and compositions for forming porous low refractive index (RI) coatings on substrates.
2. Description of the Related Art
Coatings that provide low reflectivity or a high percent transmission over a broad wavelength range of light are desirable in many applications including semiconductor device manufacturing, solar cell manufacturing, glass manufacturing, and energy cell manufacturing. The transmission of light through a material causes the wavelength of the light to change, a process known as refraction, while the frequency remains unchanged thus changing the speed of light in the material. The refractive index of a material is a measure of the speed of light in that material which is generally expressed as a ratio of the speed of light in vacuum relative to that in the material. Low reflectivity coatings generally have an optimized refractive index (n) in between air (n=1) and glass (n˜1.5).
An antireflective (AR) coating is a type of low reflectivity coating applied to the surface of a transparent article to reduce reflectance of visible light from the article and enhance the transmission of such light into or through the article thus decreasing the refractive index. One method for decreasing the refractive index and enhancing the transmission of light through an AR coating is to increase the porosity of the antireflective coating. Porosity is a measure of the void spaces in a material. Although such antireflective coatings have been generally effective in providing reduced reflectivity over the visible spectrum, the coatings have suffered from deficiencies when used in certain applications. For example, it is often difficult to control pore size and shape. Further, porous AR coatings which are used in solar applications are highly susceptible to moisture absorption. Moisture absorption may lead to an increase in refractive index of the AR coating and corresponding reduction in light transmission.
Thus, there is a need for low refractive index AR coatings which exhibit increased durability and controllable pore size.